This invention relates to a power source system adapted for mounting on a portable equipment such as a note-type personal computer and the like, and more particularly to a power system employing a microminiaturized type polymer electrolyte fuel cell which uses hydrogen as fuel and uses air as an oxidant.
With respect to examples using a fuel cell as a portable power source, Japanese Patent Unexamined Publication Nos. 4-308662 and 6-60894 disclose a series of prior art techniques, in which a phosphoric acid fuel cell is driven by hydrogen, supplied from a hydrogen storing alloy, and air. Also, Japanese Patent Unexamined Publication Nos. 54-22537 and 2-260371 disclose a construction, in which a polymer electrolyte fuel cell is driven by hydrogen, supplied from a hydrogen storing alloy, and air. U.S. Pat. No. 5,200,278 discloses a small-sized power source system, which though not portable, can be transported, and comprises a polymer electrolyte fuel cell, and in which formed water is recovered and is used as cooling water and humidifying water. In this system, a humidifying section for fuel and an oxidant is constructed integrally by a power-generating section of a lamination and end plates. In this humidifying section, the fuel or the oxidant is supplied to one side of an ion exchange membrane while water is supplied to the other side, and the membrane allows only moisture or water to pass therethrough, and utilizing this nature, the fuel or the oxidant is humidified. There have been proposed various other humidifying methods. For example, Japanese Patent Unexamined Publication No. 5-54900 discloses a humidifying method using either a power spray having a pressurized water spray nozzle provided in a supply passage for fuel or oxidant gas, or an ultrasonic humidifier having a water surface of a fined spray. Japanese Patent Unexamined Publication No. 6-338338 discloses a humidifying method, in which a porous fuel flow-field plate or a porous oxidant flow-field plate is provided between a separator plate and a unit cell, and water is supplied into the flow-field plate, thereby effecting humidification through fine holes in the flow-field plate. Japanese Patent Unexamined Publication No. 7-245116 discloses a construction, in which a humidifier using hollow membranes is provided in a stack of stacked cells to make a fuel cell compact.
However, in the above conventional portable fuel cells and polymer electrolyte fuel cell systems, a construction for mounting the fuel cell or the system on a portable equipment, as well as a construction for achieving compactness, has not been taken into consideration. For example, in the series of techniques described in Japanese Patent Unexamined Publications Nos. 4-308662 and 6-60894, various constructions for driving a fuel cell by the use of hydrogen produced from a hydrogen storing alloy are disclosed. In this system, however, since a phosphoric acid fuel cell is used, a special construction for operating a polymer electrolyte fuel cell including a humidifying mechanism is not taken into consideration. Although Japanese Patent Unexamined Publications Nos. 54-22537 and 2-260371 disclose the construction, in which the polymer electrolyte fuel cell is driven by hydrogen supplied from the hydrogen storing alloy, these publications disclose only the construction for transferring heat of the fuel cell to the hydrogen storing alloy, a wick member for recovering the formed water, and a water-permeable member but do not disclose a construction for miniaturization. Although various descriptions, relating to the constructions of the polymer electrolyte fuel cell and the system, are given in U.S. Pat. No. 5,200,278, a construction designed for mounting the system on an equipment, as well as a construction for miniaturization, is not suggested.
The humidifying methods disclosed in the above prior art techniques are problematic in that a water piping is complicated, the system itself requires an auxiliary power, and a construction for miniaturization, including a construction for recovering the formed water.
Generation of electricity by a fuel cell is accompanied by generation of heat. A polymer electrolyte, when containing water or moisture, exhibits a proton-conducting nature, and therefore when the polymer electrolyte is dried to be lowered in water content as the fuel cell generates heat, an internal resistance of the fuel cell increases to lower a power-generating ability of the fuel cell. Therefore, in order to prevent drying of the polymer electrolyte, the fuel cell needs to be cooled. On the other hand, a process of emission of hydrogen from a hydrogen storing alloy is an endothermic reaction, and so the hydrogen storing alloy, when supplying hydrogen fuel, is lowered in temperature. A hydrogen-emitting ability of the hydrogen storing alloy is lowered as the temperature lowers, and therefore in order to secure a sufficient flow rate of hydrogen, the hydrogen storing alloy needs to be heated. Therefore, it has been proposed to utilize heat, generated from the fuel cell, for heating the hydrogen storing alloy.
For example, Japanese Patent Unexamined Publication No. 2-260371 discloses a method, in which waste heat of the fuel cell is transferred to a hydrogen storing alloy container through direct heat transfer of separator plates of the fuel cell. Japanese Patent Unexamined Publication No. 6-60894 discloses a construction, in which an exhaust gas of the fuel cell passes around a hydrogen storing alloy container. Further, Japanese Patent Unexamined Publication No. 6-60895 discloses a construction, in which passage opening control means is provided in an exhaust gas passage, extending from a fuel cell body to a hydrogen storing alloy container, so as to adjust a heat transfer rate, thereby controlling a pressure of hydrogen.
However, in the above conventional portable fuel cells and polymer electrolyte fuel cell systems, a more efficient heat transfer construction for miniaturization necessary for mounting the fuel cell system on an equipment, has not been taken into consideration. For example, in the series of techniques described in Japanese Patent Unexamined Publications Nos. 6-60894 and 6-60895, there is disclosed a construction, in which waste heat of the fuel cell is transferred or transmitted to the hydrogen storing alloy container only by an air flow. However, in a microminiaturized system adapted for mounting on an equipment, to which the present invention is directed, a sufficient space for a path of such air flow is not ensured, so that the thermal transfer efficiency is not sufficient. Japanese Patent Unexamined Publication No. 2-260371 discloses a construction, in which heat is transferred directly to the hydrogen storing alloy container through thermal transfer of the separator plates. However, when the electrically-conductive separator plates are connected directly to the container, generated electricity flows into the container. Namely, there has been encountered a problem that it is difficult to secure sufficient thermal transfer in a limited volume while making the two contrary characteristics, that is, maintenance of an electrically-insulated condition of each separator plate and transfer of heat generated by each unit cell, compatible with each other.